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0 (RECEIVER) Q (RECEIVER) a (TRANSMTTTER) DIVIDER RESET(NOR 70s 124) FF7l6 United States Patent 3,445,587 RECORDING STYLUS CONTROL SYSTEMFrancis J. Jansen, Monterey Park, Robert W. Reynolds, Los Angeles, andGeorge T. Shimabukuro, Monterey Park, Calif., assigrrors to XeroxCorporation, Rochester,

N.Y., a corporation of New York Filed Oct. 1, 1965, Ser. No. 492,195Int. Cl. H04n /76 US. Cl. 178-6.6 3 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to facsimile equipment and more particularly tofacsimile transceivers adapted to operate through the direct distancedialing telephone network either with or without direct electricalconnection thereto.

Facsimile transmission is old in the art. In the past, it has mostlybeen used for transmitting photographic type of information overpredetermined leased transmission channels. More recently, equipment hasbeen marketed for the high speed transmission of documents over broadband transmission channels. The presentinvention is particularlyconcerned with the economical and flexible transmission of letters,drawings and other black-white documents over ordinary voice gradetelephone channels.

The equipment meeting these goals should be inexpensive and theinvention accordingly, provides a facsimile transceiver wherein many ofthe components are shared between the transmitting and receivingfunction, instead of a separate transmitter and receiver.

It is desirable that the equipment be capable of transmitting documentsto any location where telephones are available. The invention provides afacsimile transceiver which is capable of either transmitting orreceiving documents through any conventional telephone set withoutrequiring an electrical connection thereto. The invention provides afacsimile transceiver capable of establishing synchronism with a liketransceiver at a remote location independently of the character,frequency, or phase of the power line to which each may be connected.

The equipment should minimize the telephone charges associated with thetransmission of the document. The invention provides equipment whichdoes not require the operator to lease a so-called data set from thetelephone company, which transmits documents in a shorter time than hasheretofore been possible, and which permits the equipment operators ateach end of the transmission link to terminate the telephone connectionas soon as the connection is no longer actually needed or whenevertransmission becomes unintelligible.

The equipment should also be capable of operating through telephonecompany data sets Where available, to take advantage of their improvedtransmission capability. The invention provides a facsimile transceiverwhich operates with two level signals which will interface with aconventional data set intended for the transmission of digital signalsthrough telephone lines.

The equipment should function reliably without regard to the skill ofthe operator. The invention provides a facsimile transceiver whichrequires only the insertion of a piece of paper and the dialing of atelephone call in order to provide high quality facsimile transmission.

Specific objectives will become apparent in connection with a moredetailed description of the invention and the drawings related thereto.

"ice

FIGURE 1 is an exterior view of a facsimile transceiver according to theinvention.

FIGURE 2 is a block diagram illustrating the functions of the invention.

FIGURE 3 is a simplified isometric view of the recording mechanism.

FIGURE 4 is a simplified isometric view of the transmitting mechanism.

FIGURE 5 illustrates logical circuit elements used in the subsequentfigures.

FIGURE 6 shows the basic timing circuit.

FIGURE 7 shows the repetitive waveforms corresponding to FIGURE 6.

FIGURE 8 shows the transmitter and telephone trans ducer controls.

FIGURE 9 shows the transmitter logical circuitry.

FIGURE 10 shows waveforms generated in the circuit of FIGURE 9.

FIGURE 11 shows a video amplifier circuit used in FIGURES 9 and 10.

FIGURE 12 shows the printer power and control circuits.

FIGURE 13 shows an alternate form of FIGURE 12.

FIGURE 14 shows the stepping motor drive amplifier.

FIGURE 15 shows the printer logical circuits.

FIGURE 16 shows Waveforms illustrating the achievement ofsynchronization.

FIGURE 1 shows the external appearance of a form of facsimiletransceiver according to the invention. The apparatus is enclosed by acabinet including a generally horizontal aperture 121 in its forwardlyfacing surface. Visible within the aperture is a rotatable drum 122including a clamp bar 123. Aperture 121 permits access to the drum sothat an operator may fasten a sheet of paper to the drum to make afacsimile recording thereon. On top of the cabinet is a tray 124 forholding a document to be transmitted and feeding it through a slot 125into the scanner mechanism 126. Cabinet 120 also includes a reset buttonand an indicator light 131. Adjacent to the cabinet 120 and connectedthereto is a box 127 which is adapted to contain a standard telephonehand set and is provided with a hinged cover 128 and latch 129.

FIGURE 2 is a schematic diagram showing, in general terms, how two ofthe facsimile transceivers of FIGURE 1, each at a different location,may be interconnected to form a bidirectional facsimile system. Itshould be understood however, that the functional blocks shown in FIG-URE 2 correspond in only a very general way to the circuits or circuitfunctions described in subsequent figures. The first step in sending adocument is for the operator at one location to use his telephone todial the corresponding telephone 135 at the other location, generallythrough one or more intervening telephone exchanges 136. After a normalvoice connection has been confirmed by the operator at each piece ofequipment, each operator places his handset 137 in box 127 and closesthe cover. Either operator inserts a document through slot 125 into thescanner 126 of his unit. Scanner 126 then sends a control signal totransmit/ receive circuit which, responsive to the document in scanner126 and the handset in box 127, adapts the transceiver to the transmitmode. Scanner 126 also sends video signals to transmitter 138 whichprocesses the signals and uses them to control the operation of scanner126. Meanwhile, transmitter 138 combines the video signals with controlsignals for transmit/receive circuit 140 and introduces them intohandset 137 from which they are transmitted over the telephone line. Atthe same time, even though transmitting is taking place, timing andpower circuit 139 is exchanging signals with printer 142 and generating3 further signals for processing by transmit/receive circuit 140.

At the other transceiver a signal is picked up from the correspondinghandset 137 and detected by receiver 141 which causes transmit/receivecircuit 140 to put the transceiver into the receive mode. The receivedsignals also cause transmit/receive circuit 140 to control the operationof timing and power circuit 139 so as to bring printer 142 intosynchronism with scanner 126 of the transmitting transceiver. Thereceived signals are applied to printer 142 and cause it to record afacsimile of the transmitted document.

At each transceiver a supervisory circuit 143 monitors the operation ofthe various circuits so that a corresponding alarm sounds at each of thetwo transceivers when a transmission is either completed or interrupted.The alarm signals each of the two operators to lift up their handsetsand talk to each other to determine whether documents are to beretransmitted, more documents are to be transmitted in either direction,or Whether the telephone connection should be terminated.

It is obvious from the preceding description that an unlimited number offacsimile transceivers according to the invention may be used inconnection with each other, since any one can be functionally connectedwith any other, for either transmitting or receiving, through theconventional switching facilities of the telephone companies. Conferencecall arrangements may also be used to permit one transceiver tosimultaneously transmit to a number of others.

FIGURE 3 is a simplified isometric view of the printing or recordingmechanism. Drum 122 is journaled for rotation in bearings, not shown,and is driven through gears 151, 152 and 153 by motor 150 which ispreferably, although not necessarily a two pole synchronous motor withmeans, for example a permanent magnet rotor for providing a predictablerelationship between electrical power phase and rotational phase. Motor150 bears a pinion 151 which drives idler gear 152 at a 2 to 1 reductionratio, and idler gear 152 drives drum gear 153 at a to 1 reductionratio. Attached to drum 122 are a pair of cams 162 and 163 which actuateswitches 164 and 165 respectively. The functions of these switches willbe described subsequently in connection with a description of FIGURES 6and 12. A pen carriage 154 is located adjacent to drum 122 and slideablymounted on rails 155 which are parallel to each other and to drum 122.The pen carriage 154 carries a marking tip 156 which may be urged intocontact with the drum by an electromagnetic assembly 157 and urged awayfrom the drum by spring 158. A flexible electrical cable 166 carriescontrol voltages to the electromagnet assembly 157 and to marking tip156 itself. The pen carriage 154 also engages a lead screw 159 which isincrementally driven by either a forward stepping motor 160 or reversestepping motor 161, the two stepping motors being connected to eachother and to the lead screw. In this manner, marking tip 156 can beadvanced in uniform discrete increments on the order of 0.01 inch in adirection parallel to the axis of the drum in response to commandsderived from circuitry which will be described later on.

Marking tip 156 may take many different forms as is known in the art. Itmay comprise an electrically insulated metal stylus adapted to writedirectly upon conventional electrolytic facsimile recording paper. Thesame form of stylus can be used to deposit electrostatic charge on aninsulating sheet for subsequent development by known xerographictechniques. A simple metal stylus can also be used to record directly onpressure sensitive recording paper through selective energization ofelectromagnet assembly 157. Various forms of apparatus for the selectivedeposition of liquid ink may be employed. A variable intensity focusedlight source may also be employed for forming a latent image on a sheetof photographic paper or the like. Any of these methods or any othersuitable facsimile recording technique may be employed with theinvention.

FIGURE 4 is a simplified isometric view of a form of scanning mechanism126. A pair of drive rolls 176 is provided with cog wheels 177, as is astepping motor 178 which may be identical with motor or 161 of FIGURE 3.Motor 178 incrementally drives rolls 176 through a so-called timing orcogged belt 179. Each drive roll 176 cooperates with a pinch roller 180immediately above it to feed a sheet of paper through the scanner inincrements on the order of 0.01 inch. Fluorescent lamps 181, preferablyoperated by direct current, are positioned beneath drive rolls 176 andare provided with reflectors, not shown in this figure, to direct lightupwardly against the lower surface of a sheet of paper passing throughthe rolls, and supported on a slit-containing platen, also not shown inthis figure. A mirror galvanometer 183, including a small mirror, 184,samples light reflected from the sheet of paper and passes it throughlens to photomultiplier 186 or other photosensitive device. Since themirror galvanometer is a device adapted to rotationally oscillate themirror about an axis, the photomultiplier 186 is enabled to scan asampling spot back and forth in a line across a document or other sheetof paper passing through the drive rolls.

FIGURE 5 illustrates certain forms of elementary logic circuits whichare widely used in subsequent figures of this specification. FIGURE 5Ashows the NAND and NOR gate symbols and a suitable transistor circuitfor realizing the function represented by the symbols. The illustratedNAND and NOR symbols actually denote the same circuit function, asshown, for example, in MIL- STD-806B, Feb. 26, 1962. In terms of theillustrated transistor circuit, the symbols represent the followingfunction: the output voltage is minus 6 volts if, and only if, allinputs are at zero volts, otherwise the output is at zero volts. It isconvenient to regard most of the gates in later figures as NAND gateswith 1 equal to zero volts and 0 equal to minus 6 volts. FIG. 5B showshow two of the circuits of FIGURE 5A can be cross-coupled to provide aflip-flop circuit. The flip-flop is characterized in that it will changestate only when an input voltage of minus 6 volts is applied to theappropriate input terminal. Specifically, if minus 6 volts is applied tothe Reset input, then the flip-flop will be Set, i.e., the 1 output willbe at zero volts and the 0 output will be at minus 6 volts. FIGURE 5Cshows an obvious and self-explanatory modification of FIGURE 5B in whichthe flip-flop can be set to one of its states by a voltage of minus 6volts applied to either of two corresponding inputs. FIG- URE 5D showshow an inverter function is provided by the logic gate of FIG. 5A.FIGURE 5E shows a trigger flip-flop which changes state as a result of apulse applied to the single input terminal. In the form used in thisspecification, the input signal is a six volt positive going pulse andthe output voltages are either zero or minus 6 volts. The illustratedtransistor embodiments of the described circuit functions can beobtained in module form from the Engineered Electronics Company of SantaAna, Calif. The NAND/ NOR circuit is their model Q-4ll or Q-421 and thecircuit of 5B represents two model Q-412 or Q-422.

The symbols and circuits of FIGURE 5 represent those chosen for use inthe illustrative embodiment of the invention. The functions representedby the logic symbols can be realized by circuits of many formsobtainable from numerous manufacturers and all of which are well knownin the art. Those skilled in the art will also realize that logicalcircuitry of the type to be shown in subsequent :figures has a certainoverall input-output relation which can be duplicated using differentarrangements of the same basic logical elements and furthermore, thatthis function can be realized using quite different types of logicelements which need not even be electronic.

Merely as an illustration it may be noted that AND/ OR gates may besubstituted for the illustrated NAND/ NOR gates and that it might evenbe possible thereby to simplify the described embodiment of theinvention. In general, the designer will choose the type and design ofhis logical building blocks based on such considerations as cost, size,reliability, voltage and current requirements, speed, fan-in and tan-outcapabilities, etc.

Timing circuits FIGURE 6 shows the timing circuits used to generate thetiming waveforms shown in FIGURE 7, which are used in controlling theoperation of the facsimile transceiver. A tuning fork or other stableoscillator 201 provides a 3840 cycle output frequency which is processedby pulse shaping circuit 202 to provide a train of positivegoing pulsesat the oscillator frequency. These pulses are applied to a counter ordivider chain of seven sequentially connected trigger flip-flopsidentified as I through VII. A higher frequency crystal oscillator withadditional dividers may also be employed. For convenience the first sixstages only are regarded as constituting a distinct scale of 64 counter203 and are so shown in the figure. Each counter can be simultaneouslyreset to zero from a common source through coupling diodes 204, but thereset function will not be described except in connection with FIGURE15. The output of stage V1 is a 60-cycle square wave identified assignal A which is used to drive motor 150 as shown in FIGURES 3, 12 and13. The output of stage VII is a 30-cycle square wave H. Motor 150rotates at 3600 r.p.m. and drives drum 122 at 180 rpm. so that onerevolution requires 333 /3 milliseconds or 20 cycles of signal A. Drum122, acting through cams 162 and 163 and switches 164 and 165 generatestiming signals M, M and S in a manner which will be more fully shown inFIGURE 12. In terms of the rotation of drum 122, signal M is in the zerovolt or logical 1 state from 355.5 to 7.5 and S is in the 1 state from22 to 36. Signal M is simply the inverse of signal M. For reasons whichwill become apparent later, the otherwise arbitrary zero degree positionof drum 122 should be chosen at a point where marking tip 156 is overclamp bar 123. Because of the fixed relationship existing betweenfrequency divider 203 and drum 122 it is convenient to use the angularposition of drum 122 for specifying the various waveforms generated inFIGURE 6. For convenience it may be noted that in the illustratedembodiment one cycle of oscillator 201 corresponds to .26 millisecondand also corresponds to .28 of rotation of drum 122. Thus, one degree ofrotation corresponds to about .93 millisecond.

The outputs of stages III and IV of counter 203 are combined in NANDgate 205, the output of which is inverted by inverter 210, delayedslightly by capacitor 224 and applied to AND gate 215. This signal is inthe logical 1 state whenever counter 203 is at counts 0 to 3, 16 to 19,32 to 35, or 48 to 51. Further processing of this signal will bedescribed later.

The 0 outputs of stages V and VI of the counter are combined in AND gate206 and the resulting signal inverted to provide signal D which is inthe logical 1 state whenever divider 203 registers counts zero throughfifteen, inclusive. This output, accordingly, appears .20 times perrevolution at 0 to 4.5; 18 to 225; 36 to 40.5 etc. and is referred to asthe advance clock signal.

The 0 output of stage V is combined with the 1 output of stage VI ingate 207, the output of which is inverted in inverter 212 to provide asignal which is at the logical 1 level during counts 32 to 47 inclusive.This signal is combined in NAND gate 217 with incoming signal S which isat the 1 level from 22 to 36. The output of gate 217, inverted byinverter 228, is a signal which is at the logical 1 level from 27 to 315only and is identified as the prevideo signal G.

The 1 outputs of stages V and VI are combined in 6 NAND gate 208 toprovide a signal which is at the logical 0" level when counter 203register counts 48 to 63 inclusive. This signal is identified as F andis in the logical 1 level from 0 to 13.5; 18 to 31.5; 36 to 49.5", etc.This signal is also inverted in inverter 213 to provide a signal whichis at the logical 1 level from 13.5 to 18; 315 to 36 etc. and is usedinternally as an input to gates 218, 220, 221, 222 and 223. The otherinput to gate 218 is the 1 input of stage IV. Accordingly, the output ofgate 218 is the triple coincidence of counter stages IV, V, VI. This isinverted in inverter 229 to provide a signal which is at the logical 1level for counts 50 to 63 inclusive or 15% to 18; 33% to 36; 51% to 54,etc.

The triple coincidence of the 1 output of stages IV, V, VI is alsodetected in gate 209, inverted in inverter 214, combined in gate 219with the 1 outputs of stages II and III and finally, inverted ininverter 230. The resulting signal is accordingly at the logical 1 levelfor counts 62 through 63 inclusive. This signal is identified as L andappears from 359.4 to 360; 17.6 to 18; 35.6 to 36 etc.

The output of inverter 213 is also combined in gate 220 with signal S toproduce a minus 6 volt output pulse extending from 3l.5 to 36. Thispulse is applied to one input of flip-flop 231. The output of inverter213 is also combined in gate 221 with signal M to produce a minus 6-voltsignal extending from 355.5 to 0. This pulse is applied to the otherinput of flip-flop 231. Inasmuch as the flip-flop is alternately set andreset by the signals at pearing at its two input terminals, a signal atthe appropriate output terminal will be at the logical one level from31.5 to 355.5 This signal is designated as video gate signal I. Theoutput of gate 221 is also inverted in inverter 132 to form a signalwhich is at the logical 1 level from 355.5 to 0 and which is referred toas video end signal E.

The output of inverter 213 is also applied to the first inputs of NANDgates 222 and 223, the outputs of which are connected to opposite inputterminals of a flip-flop 233. The second input of gate 222 is connectedto the signal M while the second input of gate 223 is ounnected to theinverse of signal M, namely 1W. Thus, flip-flop 233 changes state everytime signal M changes state, but the change is delayed in each instanceuntil a logical l signal is received from inverter 213. Accordingly,flip-flop 233 changes state at 355.5 and 13.5", rather than at 352.5 and7.5 The output of flip-flop 233, extending from 355.5 to 13.5 isdesignated signal N.

Returning to the previously described signal D, this signal is combinedin gate 216 with signal M which acts as a window to permit only one Dsignal per revolution to pass through. The resulting signal is invertedby inverter 227 and constitutes a signal B, which is at the logical 1level from 0 to 4.5 only. The output of gate 216 is also applied to adelay multivibrator circuit 225 which delays it for nearly a fullrevolution of drum 122 to provide the signal Q shown in FIGURE 7.

Signal B is also combined in gate 215 with the previously describedoutput of inverter 210. The negative output of gate 215 thus extendsonly from counts 0 to 3 of counter 203 and only at the zero degreeposition of drum 122. The resulting signal is inverted in inverter 226to produce a signal designated C which is at the logical 1 level from 0to 1.13 only.

FIGURE 7 shows the above-described waveforms plus a synthesized waveformD E which is the coincidence of the previously described I signal andthe inverse of the described D signal. This composite signal extendsfrom 4.5 to 135; 225 to 31.5 etc. This particular waveform will be usedin connection with FIGURE 9 together with certain other illustratedwaveforms.

Transmitting circuits FIGURE 8 shows the scanner and telephoneassemblies schematically in somewhat greater detail, together with theirassociated circuitry. It can be seen that the fluorescent lamps 181,shown previously in FIGURE 4, are provided with reflectors 301 and thata platen 302 is provided to support a document face down as it passesthrough the drive and pinch rolls 176 and 180. A slit 303 is provided inthe platen between the lamps and immediately over the mirrorgalvanometer 183. Also shown in this figure is an aperture or stop 304which is positioned between lens 185 and photomultiplier 186 to limitand define the size of the sampling area which is scanned back and forthacross the document by mirror galvanometer 183.

Mirror galvanometer 183 may be any suitable device capable of rapidlyconverting an input signal into a corresponding rotation of a mirror.Commercially available mirror galvanometers of the type sold for use inmultichannel optical recording oscillographs represent a suitable deviceof this type. A particularly suitable device for use in the illustratedembodiment of the invention can also be made by cementing a one-halfinch diameter mirror to the pen shaft of a pen recording galvanometer,catalog No. 428647-920138, manufactured by The Brush InstrumentsDivision of the Clevite Corporation, or to the shaft of comparabledevices made by the Sanborn division of Hewlett-Packard Company.

Also shown in this figure are paper detector switches 306 and 307 whichare positioned to detect the presence of a sheet of paper in thescanner. Switch 306 detects the presence of a sheet of paper as it isfirst presented to the scanner on the left side thereof, and switch 307detects the presence of a sheet of paper within the scanner andapproximately at the position of slit 303. Switch 306 operates anassociated multi-contact relay K1 and switch 307 operates an associatedmulti-contact relay K2. Switch 307 may be replaced by a time delaycircuit actuated by switch 306. Operating power for these relays passesthrough a switch 308 which is located in telephone box 127, and which ispositioned so that it will close and pass current to relays K1 and K2only if a telephone handset is properly seated in the box. Only ifswitch 308 is properly closed will insertion of a piece of paper intothe scanner enable switch 306 to operate relay Kl. Among its otherfunctions, relay K1 transfers a contact Kla which supplies minus 6 voltsto a resistor 312, the other end of which is grounded. The voltageappearing across resistor 312 is supplied to inverter 313, the output ofwhich is a transmitter control voltage T which is at the logical 1 levelonly when relay K1 is operated. This output T is used to control theoperation of the transceiver in the transmit mode. When switch 308 isclosed but relay K1 is not energized, minus 6 volts is applied toresistor 322 instead of resistor 312. The voltage appearing acrossresistor 322 is supplied to inverter 323, the ouput of which is at thelogical 1 level only when switch 308 is closed and relay K1 is notenergized and, therefore, provides a receiver control voltage R tocontrol the operation of the transceiver in the receive mode. Relay K2has a contact (a) which holds relay K1 closed as long as relay K2 isclosed. Accordingly, relay K1 will remain closed as long as a documentis still over slit 303 and signal T will remain at the logical 1" levelfor that time. Relays K1 and K2 and other relays to be described laterare shown with their contacts in the de-energized state of the relay.The relay contacts are not necessarily shown in physical proximity tothe relay coil symbol.

Drive motor 178 is shown in association with a pair of drive coils 305.Many types of stepping motors may be used for motor 178, or motors 160and 161. They may be, for example, an ordinary electrical solenoidassociated with a pawl and ratchet drive, a rotary solenoid associatedwith a one-way drive clutch, a driving mechanism of a conventionalstepping relay, or the so-colled Cyclonome stepping motor sold by SigmaInstruments, Inc. This latter type is preferred and, as is well known,incorporates a pair of driving coils, corresponding to referencecharacter 305, which are energized alternately by means to be shown inFIGURE 14.

Photomultiplier 186 is connected to a gated squaring amplifier 321, morefully illustrated in FIGURE 11.

The energization of galvanometer 183 is controlled by a contact (b) ofrelay K2 so that the galvanometer is enabled to operate whenever adocument is in position above the slit 303. The galvanometer drive powercomes from either a prescan generator 319 or a scan generator 320, underthe control of relay K6, which is under the control of the circuits ofFIGURE 9. Scan generator 320 provides a linear ramp voltage which issynchronized with the rotation of drum 122 by means of incoming signal Ifrom FIG. 6. Prescan generator 319 filters and amplifies the incoming30-cycle square wave H from FIG. 6 to provide a 30-cycle sine wavesignal which has ten cycles or twenty half-cycles per revolution of drum122. A triangular wave would also be suitable. Suitable circuits forgenerators 319 and 320 are to be found in FIGURES 7 and 8, respectively,of S.N. 471,799, filed July 14, 1965. The reasons for providing both ahigh speed and a low speed scanning waveform will become apparent laterin the specification and are also set forth in said S.N. 471,799, filedJuly 14, 1965.

Referring to telephone box 127, there is provided a small loudspeaker309 and a soft annular gasket 310 to seal the loudspeaker 309 to themicrophone unit of handset 137. Loudspeaker 309 is connected through arelay K4 to modulator 314. Relay K4 is operated by switch 308 so as toconnect the modulator to the loudspeaker only when the transceiver is inthe transmitting mode. The modulator may be of any of the varietiesknown to the art. A highly satisfactory form of modulator comprises avoltage controlled multivibrator oscillator followed by an audioamplifier, such that sound at 1300 cycles is applied to the telephonefor one of the levels of a two-level input signal applied to themodulator, and sound of about 2300 cycles for the other input level.This arrangement has proven very satisfactory for introducing facsimilesignals into a telephone circuit without making an electrical connectionthereto. When the transceiver is not in the transmit mode, loudspeaker309 is disconnected from modulator 314 and is connected through relay K4to an alarm tone generator 315 which is controlled from the alarmcircuits of FIG- URE 13 and supplies a lower frequency sound, i.e., 800cycles, into the telephone.

An inductive pickup coil 311 is provided in telephone box 127 under theearphone end of handset 137 to pick up incoming signals. The coil may beof the shape shown and may be comprised, for example of 7900 turns of#34 insulated wire with an inductance of about 2.2 henries at 1000cycles. It has been found that there is sufiicient leakage fiux from atelephone receiver, particularly those used in the Western Electric 500subscriber set, to permit efficient signal pickup by means of theillustrated coil. As an alternative, particularly where the facsimileequipment must be used with other types of telephone instruments havingwell shielded receivers, pickup coil 311 may be replaced by a microphoneacoustically coupled to handset 137 for picking up the acoustic signalsradiated by the handset. The signals from coil 311, or from themicrophone, are demodulated in a demodulator 316 of a type appropriatefor use with the selected form of modulator 314 to produce an outputsignal corresponding to theinput signal to modulator 314. If desired,coil 311 can also be used to couple signals into a telephone fortransmission. A terminal 317 is also provided on the output side ofdemodulator 316 to permit the direct reception of facsimile signals froma telephone company data set or the like, as an alternative to signaltransmission via a conventional telephone subscriber set, as shown inFIGURE 8. A very sharply tuned, narrow band demodulator 318 is alsoconnected to pickup coil 311 to provide an output signal responsive todetection of a selected tone transmitted by alarm tone generator 315.

Voice grade telephone lines are a convenient facsimile transmissionmedium because of their universal availability, but provide a far fromideal transmission medium for facsimile or other data type signals. Forthis reason, it is desirable in modulator 314 and demodulator 316 toprovide the technical refinements which are know to the art, in order tomaximize the quality of transmitted images and the speed at which theycan be transmitted. While not a part of this invention, it has beenfound desirable to pass the facsimile signals intended fortransmissionthrough a low pass filter to eliminate'abrupt transitions and shift thesignal power spectrum toward lower frequencies and to apply thisfiltered signal to an PM or frequency shift (FSK) oscillator, such as avoltage controlled multivibrator, which has linear output frequencyversus input signal characteristics. At demodulator 316, it is desirableto employ delay equalization to compensate for the non-uniform delayversus frequency characteristics of a typical telephone channel, and toapply the resulting phase delay compensated signal to a wide bandfrequency modulation or frequency shift detector to derive a suitableoutput signal, With these refinements it is possible to achieve highquality facsimile transmission, making effective use of the nationalswitched telephone network, even allowing for the inevitable signaldegradation involved in transducing the facsimile output signal througha loudspeaker into the carbon microphone of a telephone and intransducing the input signal from an imperfect telephone receiver. Otherforms of modulation, such as amplitude modulation or vestigial sidebandmodulation may also be employed.

FIGURE 9 shows the logical circuitry which is used to control theoperation of the facsimile scanner and to generate an appropriatefacsimile signal for transmission. As an aid in understanding theoperation of the illustrated circuits, the paths of the principaltransmitted signals, as opposed to internal control signals, are shownin bold lines. There are four of these signals which are combined in afour input NOR gate consisting of gates 402 and 405, gated against thetransmit control signal in gate 406, and applied to the modulator 314,previously described in connection with FIGURE 8. A terminal 422 is alsoprovided to permit these signals to be applied directly to a data set.The first of these signals is the facsimile video signal itself, whichis a two-level signal derived by amplifier 321 from the output ofphotomultipler 186 which is, in turn, related point by point to thedensity of a document being scanned with the aid of mirror galvanometer183. This signal is gated in NAND gates 401 and 403. One of these gatingsignals is the signal I which prevents the video signal from evergetting through to NOR gate 402 in the interval from 355.5 to 31.5 ofthe drum rotation of drum 122, this period being allotted to thescanning of clamp bar 123 and for the transmission of certain controlsignal. The next signal of significance is the previously described once,per revolution prevideo signal G which is gated in NAND gate 416 by anoutput of advance control flip-flop 414. The third signal is the 20times per revolution advance clock signal D which is gated on and off inNAND gate 418 by the other output of flip-flop 414 from that used tocontrol the prevideo signal in gate 416. The fourth signal is Ti whichis a one time per revolution signal and the inverse of the previouslydescribed B signal. This signal, unlike the others, is applied directlyto the NOR gates 419 and 405 without inversion in a prior NAND gate.This signal must pass through a normally open contact of relay K1 and anormally closed contact of relay K2.

In addition to generating a composite video signal for transmission, thecircuit of FIGURE 9 generates two other important signals for internaluse. One of these signals is a composite of the D and B signals only,from the transmitted video signal. This signal is generated by means ofa NAND gate 419 which has the same input connections as NAND gate 405,and the output of which is gated in NAND gate 420 by the transmitcontrol signal, in the same manner as the composite video signal isgated by gate 406. This signal is applied, through circuits shown inFIGURE 12, to the scanner stepping motor 178, shown in FIGURE 8. Later,it will be shown that this component of the transmitted video signalcauses pen carriage 154 at a remote connected transceiver to advanceincremently in synchronism with the document advance in the transmittingtransceiver. The other signal produced in FIGURE 9 is the output of scancontrol flip-flop 410 which is applied to relay K6 in FIGURE 8 tocontrol the operation of mirror galvanometer 183 between the slow,one-linear scan per revolution mode, and the fast scan mode in whichtwenty back and forth scans are made per revolution.

The circuit of FIGURE 9 commences to function when a telephone is placedin box 127 of FIGURE 8 and a document is inserted into the scanneractuating switch 306, also of FIGURE 8. This will energize relay K1,closing contact K1a in FIGURE 9 and permitting signal T3 to pass throughnormally closed contact K20 and through gates 405 and 406 fortransmission to a remote transceiver. This same signal is alsotransmitted through gates 419 and 420 to the apparatus of FIGURE 12 fromwhich it returns to stepping motor 178 of FIGURE 8 to operate the motorat a rate of 1 incremental advance per revolution of drum 122, i.e.three advances per second. The transmitted signal under the describedconditions is shown in FIGURE 10a. When a document has advanced to theposition of switch 307, relay K2 will be energized thus opening normallyclosed contact K2c and interrupting the transmission of the B signals.At the same time, contact K2b (FIGURE 8) will close and commence thescanning operation of mirror galvanometer 183.

At this point, it is necessary to consider the signals emanating fromphotomultiplier amplifier 321 as well as the initial states of controlflip-flops 408, 410, 414 and 417. Assuming that the apparatus is to beadapted for use with ordinary document-s having black on whiteinformation, rather than the reverse, the output of amplifier 321 willbe at the logical 1 level, i.e., zero volts, when the photomultiplier islooking at a black element of the document and at the logical 0 level,i.e., minus 6 volts, when the photomultiplier is looking at a whitebackground element. Initially, i.e., before photomultiplier 186 sees anyprinted material or the like, flip-flops 408, 410, 414 and 417 will bein the 1, 0, 1, and 1 states, respectively. This can be verified byexamining a subsequent discussion of the operation of the circuit whenphotomultiplier 186 scans completely blank lines on the document afterhaving scanned lines containing marks, printing or the like. Under theinitial conditions, flip-flop 410 acting through gate 404 prevents anysignals from amplifier 321 from being transmitted and also leaves relayK6 in FIGURE 8 de-energized so that galvanometer 183 is connected toprescan generator 319. Flip-flop 414 enables D signals to pass throughgate 418 and to be transmitted through gates 405 and 406. This samesignal is also transmitted through gates 419 and 420 to operate steppingmotor 178 in FIGURE 8. Finally, flip-flop 414 also disables gate 416 andprevents prevideo signal G from being transmitted. The transmittedsignal under the described condition is shown in FIGURE 1012. Underthese conditions, the transmitted document is advanced at the rate of 60increments per second, which is 20 times as fast as lines can berecorded on drum 122. As will be shown later, pen carriage 154 isadvanced at this same rapid rate in a remotely connected matchingtransceiver.

As soon as a black area is detected in the document being scanned, theoperation of the circuit of FIGURE 9 becomes quite different. Theabsence or reduction of light falling on photomultiplier 186 causes alogical 1 output signal to be produced by squaring amplifier 321 andthis signal is enabled to pass through gate 403 to set flip-flop 408 tothe 0 state and thereby reset flip-flop 1 1 410 to the 1 state. The newstate of flip-flop 410 causes galvanometer 103 to be connected to theslow scan generator 320 rather than the fast prescan generator.

At the next coincidence of the D and F signals (see FIGURE 7) thelogical 1 level at the output of flipfiop 408 is enabled to pass throughgate 411 to set flipflop 414 to the 0 state, thereby preventing anyfurther advance clock signals D from passing through gate 418, butpermitting the next D signal to set flip-flop 408 to the 1 state throughgate 407. No further signals are transmitted until the next appearanceof prevideo signal G. The transmitted signals during a drum revolutionof this type are shown in FIGURE 100. At the next appearance of theprevideo signal G the level at the 0 output of flip-flop 414 is enabledto pass through gate 416 to set flip-flop 417 to the 0 condition and atthe same time the G signal is applied to NOR gate 402 and passes throughgate 406 for transmission. The 0 output of flipfiop 417 is applied togate 404 and directly thereafter (see FIGURE 7) video gate signal I isapplied to gate 401. The combined presence at gates 401 and 404 ofsignal I, the 0 output of flip-flop 417, and the 1 output of flip-flop410 enables the video signals from amplifier 321 to pass through gates401 and 404 and through gate 406 for transmission. The remainder of thisrevolution, or slow scan cycle, is given over to the transmission ofvideo information detected by photomultiplier 186, as shown in FIGURE d.It should be noted that the line now being scanned by galvanometer 183is the same line which was scanned once before at a more rapid rateunder control of prescan generator 319, since the initial and immediateeffect of the detection of a black area in the transmitted document wasto prevent any further advance clock pulses D from either beingtransmitted to a remote transceiver or from being applied to steppingmotor 178.

At the end of a slow scan of the type shown in FIGURE 10d, the video endsignal E passes through gate 415 and sets flip-flop 414 to the 1condition, whereby the next advance clock signal D is enabled to passthrough gate 418. At the same time, 6 sets flip-flop 417 to the 1 stateand short master signal C is enabled to pass through gate 409 to resetflip-flop 410 to the 0 state and once again enable video signals fromsquaring amplifier 321 to reach flip-flop 408. Galvanometer 183 is nowagain connected to prescan generator 319 which is phased with respect tothe slow scan generator 320 so as to provide a rapid retrace followingthe slow scan. If no black areas are detected in the document beingtransmitted during this retrace interval, the galvanometer will continueto be driven by the fast prescan generator 319 and advance clock signalD will be transmitted through gate 418 after each fast scan. Thetransmitted waveform will then be as shown in FIGURE 10d. However, assoon as a black area is detected, the circuit of FIGURE 9 will revert tothe slow scan mode already described and the transmitted signal for theremainder of the slow scan cycle will be as in FIGURE 10c. If a blackarea is detected along the very next scan line the transmitted waveformwill be as in FIGURE l0e.

The operation of the facsimile transceiver in the transmit mode can nowbe described in a simpler way. In the absence of black areas or othermarks which the photomultiplier and amplifier are designed to detect, adocument will be rapidly scanned alternately from left to right and fromright to left. No video information will be transmitted in thiscondition but characteristic advance signals will be transmitted andwill also be directed to the transmitter stepping motor to advance adocument one increment at the end of each scan. If a black area isdetected during a fast scan, then the document is not advanced anyfurther, a document advance signal is not transmitted, and the scanningaction reverts to the slow mode. When the scanning mechanism, i.e.,galvanometer 183, reaches the time and position at which a slow scan isabout to commence, a characteristic prevideo alerting signal istransmitted and thereafter video signals corresponding to the scan aretransmitted. At the end of the slow scan the document is advanced oneincrement, a paper advance signal is transmitted, and the galvanometerexecutes a rapid retrace during which video signals are not transmitted.If information is detected during the retrace, then a further slow scanis made and further paper advances or advance signals are withheld untilthe end of the slow scan. If no information is detected during the fastscan retrace, then the document is advanced at the end of the retrace,an advanced signal is transmitted, and further rapid scans and advancesare made until such time as black areas or other information aredetected. In this way, every elemental line of the document whichcontains information is scanned twice, first with a rapid scan and thenwith a slow scan during which video signals are transmitted. Linesbearing no information are merely scanned rapidly once. In this way adocument can be scanned many times more rapidly than as usual where allareas of the document are scanned at normal speeds compatible with thetransmission medium being employed, i.e., a telephone circuit. It willbe appreciated that when scanning printed matter and particularlytypewritten letters and the like, the majority of the scan lines willtraverse only blank paper.

In a typical facsimile transceiver corresponding to the illustratedembodiment, the vertical resolution will be on the order of scan linesper inch and the horizontal resolution, along the scan lines, will beapproximately the same. This level of resolution is generally acceptedas being adequate for transmitting printing, typing, handwriting,drawings and the like without loss of information and with anaesthetically acceptable level of quality. Increasing the resolutionincreases the quality of reproduced images but also increases the timerequired to transmit a document. It has been found, on the other hand,that skipping alternate scan lines, while maintaining horizontalresolution unaltered, halves the time required to transmit a documentand provides intelligible, if less pleasing, facsimile copies where theoriginal subject matter is in the nature of printing or typing. Meansare provided to accomplish this result solely at the discretion of thetransmitter operator by including switch 421, gate 412 and inverter 413.With switch 421 open the circuit of FIGURE 9 operates as previouslydescribed. In particular, at the end of a slow scan flip-flop 414 is setto permit a single advance clock pulse D at the 0 degree position to betransmitted and to actuate stepping motor 178. Immediately after thispulse has been transmitted the D F signal passes through gate 411,resets flip-flop 414, and prevents the next D signal from passingthrough gate 418. With switch 421 closed, however, inverter 413 isconnected with gate 411 and the two together function as a four inputNAND gate. Now, the

30-cycle square wave, signal H, is inverted in gate 412 and applied toinverter 413 and prevents the reset signal from being applied toflip-flop 414 during the critical period from 18 to 36 of rotation ofdrum 122. This is the period in which the second D pulse appears.Accordingly, in this mode of operation two consecutive advance pulsesare transmitted and also applied to stepping motor 178 before prevideosignal G is transmitted. A typical transmitted waveform in this mode ofoperation is shown in FIGURE 10 Thus, a document receives twoincremental advances between each slow scan.

The double skipping feature is valuable as described but may causenarrow horizontal lines or the like to be completely missed when thetransmitter is operating in this double skipping mode. The reference tonarrow horizontal lines is intended to cover those markings which wouldbe detected along only a single scan line. With the transceiveroperating in the fast skipping mode as shown in FIGURE 10b, detection ofinformation will cause the flip-flop 414 to be reset almost immediatelyand prevent 13 further transmission of advance clock signals D, as shownin FIGURE 100. With switch 421 closed, however, there would ordinarilybe a 50% probability that the signal H would be at the wrong level andthus delay the resetting of flip-flop 41-4 and permitting thetransmission of one additional advance clock signal D. The ensuing slowscan would therefore not be of the line in which the information wasdetected but instead the next subsequent line. This situation issubstantially prevented by connecting the signal? to the other terminalof gate 412, which is conveniently considered as a NOR gate. When doubleskipping from one black containing line to another the circuit worksexactly as previously described, T being at the volt level in therelevant time interval. However, when information is first detectedwithin a sequence of fast scans,Twill be at the minus 6 volt level, andE will be enabled to reset advance control flip-flop 41-4 regardless ofthe state of signal F, thus preventing the transmission of furtheradvance signals D.

FIGURE 11 is a simplified schematic diagram of the photomultiplieramplifier 321. An inverting voltage amplifier 501 amplifies thephotomultiplier output and provides a signal which is more positive whenthe photomultiplier looks at a white or background area and morenegative when it looks at a black area. This output signal is coupled toground through capacitor 502 and rectifier 503 which together functionas a peak rectifier providing an output voltage clamped to zero volts inbackground areas and negative in black areas. This voltage is coupled byresistors 505 and 506 to the normally positively biased base of pnptransistor 507. When the photomultiplier looks at a black area amplifier501 will produce a negative output signal which, will cause transistor507 to conduct and develop a 0 output from limiting postamplifier 508.At other times the output of amplifier 508 is limited to minus 6 volts.During the time that photomultiplier 186 would otherwise be looking atthe edges of a document or other portions which are not transmitted,transistor 504 is gated off by signal I as a result of which capacitor502 is not further charged but holds its charge in accordance with thetime constant determined by its value and that of resistors 505- and506, i.e., remembers the background level. Accordingly, the output fromamplifier 321 is a signal which is reliably at the preselected logical 1value when black is being scanned and logical 0 when white is beingscanned. It will be realized that more complex black/white decisionmaking circuitry may also be employed such as that disclosed incopending applications Ser. No. 329,640, filed Dec. 11, 1963, now PatentNo. 3,394,222, issued July 23, 1968, or Ser. No. 461,693, filed June 7,1965.

Receiver and alarm circuits FIGURE 12 shows the power and controlcircuits of the printer portion of the transceiver. Recording drum 1122is driven by a motor 150 as already shown in FIG- URE 3. Motor 150 isoperated by signal A from FIGURE 6, after suitable amplification by apower amplifier 601. Pen carriage 154 is mounted on a lead screw 159driven by stepping motors 160 and 161 as also shown in FIG- URE 3. Inthis figure, the individual drive coils 606 for motor 160 and 607 formotor 161 are shown. The stepping motors used to incrementally drivelead screw 159 may be of any suitable type as disclosed in connectionwith stepping motor 178. In the described embodiment stepping motors 160and 161 may be of the Cyclonome type manufactured by Sigma Instruments,as previously described in connection with stepping motor .178. Aunitary assembly of two of these uni-directional stepping motors mountedback-to-back on a common shaft is available under the designation model9AH. The stepping motors are driven by pulses applied in alternation tothe two drive coils and a special amplifier 608, shown in greater detailin FIGURE 14, is provided to generate the necessary drive 14 pulses. Theoutput of this amplifier is connected to contacts b and c of relay K1(FIGURE 8) which direct the pulses to either the recorder steppingmotors of FIGURE 12 or the transmitter stepping motor of FIGURE 8. Whena document is not being transmitted relay K1 will not be energized andthe contacts will be in the illustrated position wherein ampliffier 608is connected to the printing components rather than the transmittingcomponents.

A further set of relay contacts KM and K3e determine whether the pulsesare applied to forward stepping motor or reverse stepping motor 161.Relay K3 is illustrated in this figure and will be described. Tocomplete the description of this portion of the figure, it is noted thata further contact on relay K3 enables amplifier 608 to be driven eitherby the D pulses from FIGURE 6 or by pulses from a NOR gate 609 which isconnected both to gate 420 of FIGURE 9 and to gates 734 and 735 ofFIGURE 15, yet to be described. The pulses derived from FIGURE 9 areintended to be applied to stepping motor 178 of FIGURE 8 and this isaccomplished through previously described relay contacts Klb and Klcwhich switch the output of amplifier 60-8. The pulses from the circuitof FIGURE 15 are the pulses intended to operate stepping motor 160 andwill pass from amplifier 608 to motor 160 through the previouslydescribed relay contacts when a document is not being transmitted.

A power amplifier 610 amplifies the printing or video signal from FIGURE15 and applies it to the marking tip 156 and an amplifier 611 amplifiesthe pen engage signal from FIGURE 15 and applies it to theelectromagnetic assembly 157 of pen carriage 154.

Cams 162 and 163 are associated with drum 122 as previously shown inFIGURE 3. A voltage of minus 6 volts is applied through switch 164 togrounded resis tor 602, and through switch 165 to grounded resistor 604,the switches being actuated by cams 162 and 163 respectively. Thevoltage appearing directly across resistor 602 is the previouslydescribed control voltage H and this voltage when inverted in inverter603 is control voltage M. Similarly, the voltage across resistor 604 isinverted in inverter 605 and becomes control voltage S. These voltagesare used to control the timing circuits of FIGURE 6 and their functionshave already been described. It will be understood that there are manyother ways of deriving such control voltages from the rotation of drum122. Magnetic proximity switches, photoelectric detectors and the likecould be used equally as well as the illustrated cam operated switches.Furthermore, a switch or the like may be used to initiate a controlsignal at a desired position of drum 122 and a multivibrator circuit orthe like may then be used to determine the duration of the signal. Itwill be understood that the functions of switches 164 and 165 may beperformed through the use of additional dividing stages, gating circuitsand the like in FIGURE 6. However, the illustrated method of derivingthese signals is particularly simple, economical and reliable.

Limit switches 6.12 and 613 are positioned adjacent the ends of leadscrew 159 and are adapted to be engaged by pen carriage 154 at the leftand right limits of travel. Switch 613 has a normally open contact whichis closed by contact with the pen carriage at the end of the normaltravel of carriage 154 and switch 612 has a normally closed contactwhich is opened by the pen carriage as it returns to the startingposition. The closing of switch 613 energizes relay K3 which causescontact (a) to close and maintain relay K3 energized through a circuitincluding switch 612. The energization of relay K3 causes the input ofdrive amplifier 608 to be connected to D signals from FIGURE 6 andcauses the output of the driver amplifier to be transferred from forwardstepping motor 160 to reverse stepping motor 161. A further contact onrelay K3 causes a control voltage to be sent to the circuit of FIG- URE15, yet to be described. With relay K3 energized, pen carriage 154 isreturned rapidly to the left at the rate

